Bidirectional Forwarding Detection (BFD) is an IETF (Internet Engineering Task Force) standard that allows two endpoints to monitor reachability over a link or a network by both ends periodically sending “hello” packets to each other. It is an efficient and generic hello/keepalive protocol that is widely used by many applications, including, for example Interior Gateway Protocols (IGPs), Exterior Gateway Protocols (EGPs) and protocols such as Hot Standby Router Protocol (HSRP), Inter-Chassis Communication Protocol (ICCP), and others.
Seamless Bidirectional Forwarding Detection (S-BFD) is a simplified mechanism for using BFD with a large proportion of negotiation aspects eliminated for network continuity testing.